It has previously been proposed to provide water tanks, such a toilet cistern or a cold-water tank, with a valve which is configured to operate to shut-off the supply of water when the level of the water in the tank reaches a predetermined point. For example, it is typical in domestic applications to provide a so-called ball valve which consists of a hollow ball-shaped float that is connected to a simple valve by a movable arm.
FIG. 1 is a schematic representation of a tank 101 showing the valve components in an empty position where the amount of fluid in the tank is reduced. The tank 101 has an inlet pipe 103, an outlet pipe 105, and an overflow pipe 107. Fluid flowing through the inlet enters a valve assembly 109 that is provided (in this instance) with a flap valve 111 that is pivotally movable between an open position (as illustrated in FIG. 1) where fluid flows through the valve and out of a valve assembly outlet 113 and into the tank 101, and a closed position where fluid flow is arrested (as illustrated in FIG. 2) once a predetermined maximum water level 121 (see FIG. 2) has been reached. The flap valve 111 is coupled to a float arm 115 that has a float 117 mounted on one end, and the float arm 115 is pivotally moveable about a pivot point 119 to move the flap between the open and closed positions.
FIG. 2 is a schematic representation of the tank 101 showing the valve components in a position where the fluid in the tank is at the predetermined maximum level 121 and the float 117 has moved the float arm 115 to close the valve 111. As will be appreciated, the float 117 floats on the water in the tank 101, and as the water level and float 117 rises the arm 115 moves to close the flap valve 111 on the water inlet valve assembly 109 to shut off the supply of water to the tank. In the event of a valve failure or a failure of the float to rise with the water level, continual water supply to the tank will cause the water level in the tank to rise to a level 123 above the predetermined maximum level 121 where an “oversupply condition” is said to have occurred, and at that point the intention is that excess water should safely drain from the tank via the overflow pipe 107.
Whilst such systems have operated adequately for many years, the advent of an oversupply condition where water is being drained from the overflow pipe 107 can cause significant amounts of water to be lost and in times where water is a limited resource such escapes should be avoided or reduced wherever possible.
It is also the case that if the valve 111 or valve assembly 109 should deteriorate to a point where the volume of liquid being supplied per unit time from the inlet 103 is greater than the volume of liquid escaping via the overflow pipe 107 per unit time (or indeed if the float should fail to rise with the water level), then the tank can fill beyond its intended maximum level 121, beyond the oversupply level 123 where excess water flows down the overflow pipe, and an overflow of water over the sides of the tank 101 can occur.
In the case of appliances (such as sinks, baths, basins, bidets and the like) there are usually no shut-off devices provided. Overflow pipes are, however, usually provided and such pipes are typically linked to the drains (often via a waste pipe through which waste water normally flows) so that once the water level in the appliance has risen beyond the predetermined maximum level, additional water can escape from the appliance via the overflow pipe and a spill of water flowing over the sides of the appliance can be avoided.
However, a significant problem with these appliances is that it is often the case that the appliances are configured so that a greater water volume can be supplied per unit time than the overflow pipes can remove. In such circumstances, these appliances are reliant on the user noticing that the water level has risen beyond the maximum point and taking appropriate corrective action (e.g. by turning off the taps of the appliance) to avoid overflow of water from the appliance. If the user is distracted or is not present, then the level of water in the appliance can continue to rise until it spills out of the appliance and damage can occur.
It is possible to conceive of an electronic valve and detector system which would act to shut-off the supply of water in the event of an oversupply of water being detected, but such a system would require a supply of electricity, either from batteries or the mains, to operate. Batteries degrade over time, and as such a system that utilised a battery power source would need careful monitoring to ensure that the device has sufficient power to operate properly. Connecting such a device to mains power would require that mains power is in close proximity to the water supply, and the dangers associated with electricity and water are such that such an arrangement would best be avoided—particularly as such valve and detector systems may well be retrofitted by persons unskilled in electrical installations. It is also the case that an electrical supply may not always be available close to the appliance to which the device is to be fitted.
It would be highly advantageous, therefore, if device could be devised which did not require electricity to operate to shut-off or at least substantially restrict fluid flow in the event of an oversupply being detected.
One previously proposed attempt to provide such a device is disclosed in GB Patent Publication No. 2288330. This device includes a cold water inlet, a hot water inlet, an overflow inlet, and an overflow outlet. The cold water inlet is connected to the cold water supply and to the cold water tap of the appliance. In a similar fashion, the hot water inlet is connected to the hot water supply and to the hot water tap of the appliance. The overflow pipe of the appliance is coupled to the overflow inlet, and the overflow outlet is coupled to the drains.
The device includes a chamber into which water from the overflow inlet can flow. A float is provided within a float guide in the chamber and is connected to a pair of cantilevered actuator arms which project into the hot and cold inlets via respective access holes cut in the hot and cold inlet walls. The overflow outlet includes a bleed hole to allow liquid in the chamber to run into the drain.
When the level of water in the appliance exceeds the predetermined maximum level, the water runs into the appliance overflow pipe and via the pipe into the chamber. As water enters the chamber the water level in the chamber rises and the float moves to an elevated position. As the float moves higher the cantilevered arms in each of the hot and cold inlets progressively move to obstruct the flow of water until the flow is cut-off when the float is generally at the level of the overflow outlet.
At this position, water flow into the appliance has been prevented, and as such it is no longer possible for the appliance to overflow. However, as soon as the water in the chamber begins to bleed into the outlet waste, the water level in the chamber will reduce, the float will drop and the hot and cold water inlets will open once more until the level of water in the chamber is replenished by water flowing into the chamber via the overflow inlet.
It is apparent, therefore, that whilst this device would achieve the primary aim of preventing overflows, it necessarily cycles between open and closed valve positions, and as such it inherently wastes significant amounts of water. It is also possible, if that cycling occurs relatively quickly, for the device to cause water hammer in the pipework by generating pressure pulses in the hot and cold water inlets.
An aim of the present invention is to provide a flow-control device which reduces the chance of an overflow occurring, whilst also avoiding the problems associated with prior devices of the type disclosed in the abovementioned GB patent application.